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finishing black polyurethane

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finishing black polyurethane

Postby bridgeman » Tue Nov 24, 2015 9:22 am

Hi - I have a problem.
I'm making small parts from polyurethane into which I've stirred a small quantity of black pigment. The finish is good, apart from where the two halves of the mould are joined. There, I have to remove some excess material and then sand it smooth. That's OK except that where I sand the part, it's no longer shiny black but dullish grey. This is true however fine a grit I use (I've used 5000 grit wet and dry), or even metal polishing paste. I'm having to spray the parts black with paint which is a time consuming nuisance. Is there a way round this difficulty?
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Re: finishing black polyurethane

Postby mangozac » Wed Nov 25, 2015 7:48 am

Using a harder curing resin would help as it will polish up better. The best option though would be to see if you could make the moulds in a way to minimise the seam.
Oh yeah I can make that....
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Re: finishing black polyurethane

Postby Blindhorizon » Tue Feb 16, 2016 6:18 am

I have no experience with this but try taking a papertowel and dipping it in resin that's mixxed and then rubbing it over the sanded area. I guess the idea is to put fresh resin in the grooves of where you sanded. You want minimal resin as possible on the towel is assume. If something like this works let us know!
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